In recent years, multi-carrier transmission has been proposed that uses cyclic delay transmit (CDT) diversity that simultaneously performs transmission from a transmitter that is provided with a plurality of transmission antennas while adding a (cyclic) delay that differs for each transmission antenna (Non-patent document 1). When using this diversity method, since the frequency selectivity of channels can always be strongly achieved, excellent average bit error rate (BER) performance can be obtained.
Also, there is proposed, in Evolved UTRA and UTRAN of the 3rd Generation Partnership Project, a method of obtaining a superior average BER by adopting the aforementioned CDT diversity in a method called soft combining that can obtain a site diversity effect. In the soft combining, base stations, which are transmitters provided with a plurality of sectors, transmits signals using the same frequency and same time from transmitting antennas that belong to each sector particularly to the same receiver that is positioned near the sector edge so that a combined wave is received by the receiver side (Non-patent document 2).
FIG. 16 is a schematic drawing that shows the appearance of signals being transmitted from transmitting antennas 1a, 1b that are provided on transmitters belonging to two different sectors to a receiving antenna 2a that is provided on a receiver. As shown in the drawing, signals s1, s2 are respectively transmitted from the transmitting antenna 1a and the transmitting antenna 1b, and a combined wave is received by the receiving antenna 2a. 
FIG. 17A shows a delay profile h1 that is time-domain representation of the propagation path between the transmitting antenna 1a (FIG. 16) and the receiving antenna 2a (FIG. 16). FIG. 17B shows a delay profile h2 that is time-domain representation of the propagation path between the transmitting antenna 1b (FIG. 16) and the receiving antenna 2a (FIG. 16). In FIG. 17A and FIG. 17B, the horizontal axis denotes time and the vertical axis denotes electrical power.
The signals s11 and s12 in FIG. 17A are signals s1 that are transmitted from the transmitting antenna 1a, and represent signals that have reached the receiving antenna 2a by passing along two different propagation paths. Also, the signals s21, s22, s23 are signals s2 that are transmitted from the transmitting antenna 1b, and represent signals that have reached the receiving antenna 2a by passing along three different propagation paths.
In the case where the signals s2 transmitted from the transmitting antenna 1b are signals generated by delaying the signals s1 transmitted from the transmitting antenna 1a, that is, in the case of adopting the CDT diversity between the transmitting antenna 1a and the transmitting antenna 1b, the transmitting signals can be regarded as having reached the receiving antenna 2a (FIG. 16) by passing through a propagation path that is a combination of the delay profiles h1 and h2, as shown in FIG. 18. However, the time domain t1 of FIG. 18 corresponds to the delay profile h1 (FIG. 17A), and the time domain t2 corresponds to the delay profile h2 (FIG. 17B).
By contrast, by multiplying an orthogonal code that is unique to each sector by a subcarrier for propagation path estimation between the respective sectors in which transmitters are placed, while transmitting the subcarriers for propagation path estimation using the same frequency and same time, the subcarriers for propagation path estimation from each sector are separated on the receiver side, and so propagation path estimation is individually performed (Non-patent documents 3 and 4).
FIG. 19A shows the constitution of a signal s1 that is transmitted from the transmitting antenna 1a (FIG. 16). The signal s1 is constituted from a region r1 and a region r2. In region r1 is disposed a symbol for propagation path estimation that is a known symbol, and in region r4 is disposed a common data channel that is a data symbol.
Also, FIG. 19B shows the constitution of a signal s2 that is transmitted from the transmitting antenna 1b (FIG. 16). The signal s2 is constituted from a region r3 and a region r4. In region r1 is disposed a symbol for propagation path estimation, and in region r4 is disposed a common data channel.
The symbols for propagation path estimation that are included in the regions r1 and r3 are used to obtain the propagation path information that is required for demodulating the data that is contained in the regions r2 and r4.
FIG. 20 is a configuration drawing of the signal s3 that is transmitted from three transmitters that belong to different sectors to a receiver. The signal s3 is constituted from sub-carriers sc1 to sc12. The sub-carriers sc1 to sc4, sc5 to sc8, and sc9 to sc12 are respectively included in the frequency ranges f1, f2, f3. The signals s31 to s33 represent signals that are transmitted from transmitters that are disposed in sectors #1 to #3. Orthogonal codes C1 (1, 1, 1, 1), C2 (1, −1, 1, −1), and C3 (1, 1, −1, −1) are respectively multiplied by the signals s31 to s33.
In the frequency range f1, the signal s31 that is transmitted from the transmitter that is arranged in sector #1 is included in the addition result, but the signals s32, s32 from the transmitters respectively arranged in sectors #2 and #3 become 0. It is therefore possible to separate each signal even by performing transmission of the signals s31 to s33 using the same frequency and the same time. This situation is referred to as “the orthogonality being maintained”.
By contrast, in the case of applying the CDT diversity to the transmitting antennas that are arranged in the sectors #1 to #3, it is necessary to obtain the propagation path information from the symbols for propagation path estimation that are included in regions r1, r3 (FIG. 19A, 19B) in order to demodulate the regions r2, r4 (FIG. 19A, FIG. 19B) in the above manner. To this end, the signals that are transmitted from the transmitting antennas are normally added with the same delay to the regions r3, r4.
However, in the case of applying the CDT diversity to the transmitting antennas between sectors, since the orthogonality between orthogonal codes is lost, when attempting to separate and estimate the propagation paths between the transmitting antenna and receiving antennas of each sector using the symbols for propagation path estimation, there is the risk of an error occurring in the propagation path estimation result.
FIG. 21 is a drawing that shows the constitution of the transmission signal s4 in the case of the delay profiles h1=h2=1 in FIG. 17A and FIG. 17B, that is, a delay wave not existing and even in relation to a directly arriving wave, there is no change in the phase rotation and amplitude. The signal s4 is constituted from sub-carriers sc1 to sc12. The signals s41, s42 represent signals that are transmitted from transmitters respectively arranged in sectors #1 and #2. The code C4 (1, 1, 1, 1) is multiplied by the signals s41, 42.
Here, a description shall be given for the case of multi-carrier transmission being performed, and a delay of half of the symbol being added by the phase rotation described below between the transmission antennas 1a, 1b of FIG. 16. Also, diversity by the soft combining method shall be described for the case of being used between the transmitting antenna 1a and the transmitting antenna 1b. Here, for the time being only the signals transmitted from the transmitting antenna 1a and the transmitting antenna 1b shall be considered. Here, the soft combining method is a method of suppressing the interference component while increasing the signal component of the receiver by transmitting the same signal that is generated from the same data at the same timing from transmitters arranged in two sectors to the same receiver.
At this time, in the transmitted signals that are transmitted from the transmitting antenna 1a (FIG. 16), the phase rotation of the following Equation (1) is multiplied by the kth subcarrier.θ=2πkT/N=2πk·N/2·1/N=kπ  (1)
At this time, the signal from the transmitting antenna 1a (FIG. 16) becomes as shown in FIG. 21, and so enters a state in which the orthogonality with the transmitted signal from the transmitting antenna 1a (FIG. 16) is lost.
Note that N in the abovementioned Equation (1) denotes the number of points of the inverse fast Fourier transform (IFFT) during multi-carrier modulation, and T denotes the delay point difference (delay time difference) between two transmitting antennas.
Furthermore, non-patent document 5 discloses a transmission method that involves transmitting with a format that retains the orthogonality between sectors adding a delay (rotation) only to the data portion even in the case of performing soft combining of signals for sector propagation path estimation. Also, it discloses that the delay amount can be informed from the base station to the transmitter.
As shown in non-patent document 5, this technology is premised on receiving the subcarrier for propagation path estimation that has not been delay processed by the receiver, utilizing the orthogonality to estimate the propagation path from each transmitter, and, based on the delay amount that is notified from the base station, estimating the propagation path during soft combining.
According to this method, since the orthogonality of the preamble portion is maintained, it is possible to accurately measure the strength of radio waves from the respective base stations, and it is possible to obtain the effect of soft combining.
Non-patent document 1: “Application of Cyclic Delay Transmit Diversity to DS-CDMA using Frequency-domain Equalization”, IEICE Technical Report, RCS2004-392, March 2005.
Non-patent document 2: 3GPP, RI-050795, “Intra-Node B Macro Diversity based on Cyclic Delay Transmissions”, [Sep. 7, 2005 search], Internet (URL: ftp://ftp.3gpp.org/TSG_RAN/WG1_RL1/TSGR1—42/Docs/R1-050795.zip)
Non-patent document 3: 3GPP, RI-050704, “Orthogonal Common Pilot Channel and Scrambling Code in Evolved UTRA Downlink”, [Sep. 7, 2005 search], Internet (URL: ftp://ftp.3gpp.org/TSG_RAN/WG1_RL1/TSGR1—42/Docs/R1-050704.zip)
Non-patent document 4: 3GPP, RI-050700, “Intra-Node B Macro Diversity Using Simultaneous Transmission with Soft-combining in Evolved UTRA Downlink”, [Sep. 7, 2005 search], Internet (URL: ftp://ftp.3gpp.org/TSG_RAN/WG1_RL1/TSGR1—42/Docs/R1-050700.zip)
Non-patent document 5: 3GPP, RI-051046, “Further Details on Adaptive Cyclic Delay Diversity Scheme”, [Sep. 7, 2005 search], Internet (URL: ftp://ftp.3gpp.org/TSG_RAN/WG1_RL1/TSGR1—42bis/Docs/R1-051046.zip)
However, in the case of using the method disclosed in non-patent document 5, during soft combining, it is necessary to estimate the propagation path of the data portion by performing processing in the receiver different from during data receiving. Also, in a system that adaptively changes the delay amount, it is necessary to notify the receiver of the delay amount.